Many different liquids must be packaged and sealed under conditions that prevent contamination of the liquid by undesired particles. The liquids may be destined for use as reagents in analytical or diagnostic techniques requiring ultra-high purity or for administration as diagnostic or therapeutic pharmaceuticals. In preparing and packaging such liquids, extensive precautions are taken to prevent contamination by undesired particles. After preparation, the liquid is dispensed to containers which are then sealed. It is during packaging that contamination by undesired particles may occur in spite of precautions. These particles may render the liquid less valuable or inoperable for their intended purposes or may constitute a source of danger, in particular in a pharmaceutical liquid for parenteral administration to a patient. In these cases, examination of each container, after sealing, is a compulsory requirement.
Various measures have been suggested to inspect liquids dispensed in containers for the presence of undesired particles. A conventional examination method is a visual inspection which, although easy to perform and sufficiently reliable, is rather time-consuming. In such an inspection, the liquid is preferably illuminated with an artificial light source, either directly or indirectly. The filled containers, after the liquid has been put in motion, usually are held successively against a black and a white background, so that light-colored and dark-colored particles, if any, in the liquid become visible. In such an inspection, it is desirable to keep the inspection time per container as short as possible, without compromising the reliability of detection, merely for economic reasons. However, shortening of the time necessary for inspection is of prime importance when viewing or visually inspecting containers having a radioactive liquid for reasons of safety. Although the observer's eye is protected as well as possible during viewing from radiation by, for example, positioning a transparent shield of lead-glass between the observer and the container to be inspected, it cannot be entirely prevented. So the exposure time, i.e., the time in which the observer is exposed to radiation from the container, must be minimized.
In another usual method of inspecting liquids dispensed in containers for the presence of undesired particles, suitable illuminating means and a detection apparatus are used. By illuminating the liquid in the container in a special manner with the light of a carefully selected light source and then determining the intensity of the transmitted or scattered light by means of, for example, a photosensitive cell, a camera or a video camera with display screen, an impression can be gained about the extent to which the liquid has been contaminated with particles. Such an inspection device is disclosed in U.S. Pat. No. 4,676,650.
These and similar devices are not only complex and hence sensitive to disturbances, and expensive as regards acquisition and maintenance, but they are also not always satisfactory with regard to reliability and detection sensitivity.
It is the object of the present invention to provide a more simple and reliable means of examining liquids for impurities which can be used universally, i.e., both for visual inspection and for use with detection apparatus, and by which the examination can be facilitated so that the inspection time can be shortened as compared with the known visual inspection methods.
It is a further object to provide the means to more easily inspect liquids some time after packaging for changes such as sedimentation, crystalization, or gelling.